The current optical transport network puts higher and higher demand on the network survivability. The network survivability means ability to still retain service continuity in a case of failure in the network. An APS (Automatic Protection Switching) is important means for implementing the survivability of an optical network.
A ring network protection technology has characteristics of a high utilization ratio of the network resources and a fast protection switching and therefore has been widely applied. The ring network protection may be classified into multiplex section shared ring network protection, channel shared ring network protection and sub-wavelength shared ring network protection, etc. according to different granularities of the protection switching. For instance, G.841 of International Telecommunications Union ITU-T sets forth the principle of the multiplex section shared ring network protection of SDH (Synchronous Digital Hierarchy). The principle is: after a certain span fails in the ring network, a new ring is formed by performing a double-end switching at nodes adjacent to both ends of the failed span, so as to implement the protection function to the service. In addition, Patent of CN13131955 with the title of “Implementing Method of Protection Switching Protocol Supporting Channel Sharing Ring Protection” provides a method for realizing switching protection protocol supporting channel shared ring network protection. In the method, on the basis of three types of node states, which are an idle state IDLE, a pass-through state PASS and a switching state SWITCH, stipulated in G.841 protocol of ITU-T, three types of channel protection states being introduced, which are a channel switching state CSWITCH, a channel pass-through state CPASS and a channel idle state CIDLE; determining firstly state of each node according to the ITU-T protocol when a failure occurs; and then, judging by each node whether a protected service is affected by the failure according to the node state, protected service information and a network topological structure, so as to further determine the channel protection state, to perform protection switching action at add and drop nodes of the service, so that the protection function is implemented to the damaged service.
Regardless of the multiplex section shared ring network protection, the channel shared ring network protection and the sub-wavelength shared ring network protection, since the ring network protection structure is determined during network planning and cannot be dynamically adjusted according to the network failure state, when a plurality of spans are failed in the ring network, the services passing through the failed spans will be interrupted and other services on the ring network will also lose the protection function at the same time. It will be explained with two specific examples in the following.
FIG. 1 is a schematic diagram of one specific example of the multiplex section shared ring network protection in the prior art. The multiplex section shared ring network protection group shown in the figure consists of eight nodes, marked as A, B . . . H, respectively. A pair of services present between the node H and the node F, and a pair of services present between the node F and the node E. After a span 4 fails, the services between the node H and the node F are transmitted via a protection path thereof (the broken line in the figure represents the protection path of the services), i.e., going through the node H, the node G, the node H, the node A . . . until the node F, while the services between the node F and the node E will not be affected. However, after a span 5 also fails, since both the working path and the protection path of the two services above fail, these two services cannot be protected but in a state of interrupted service, and all the other services on the ring network will lose the protection function.
FIG. 2 is a schematic diagram of one specific example of the channel shared ring network protection in the prior art. The channel shared ring network protection group shown in the figure consists of eight nodes, marked as A, B . . . H, respectively. A pair of services present between the node H and the node F, and a pair of services present between the node F and the node E. After a span 4 fails, the services between the node H and the node F are transmitted via a protection path thereof (the broken line in the figure represents the protection path of service), i.e., going through the node H, the node A . . . until the node F, while the services between the node F and the node E will not be affected. However after a span 5 also fails, since both the working path and the protection path of the services between the node H and the node F fail, the service will be in a state of interrupted service, and meanwhile, the services between the node F and the node E will also lose the protection function.